Instrument for scanning document for quality

ABSTRACT

An apparatus to scan, detect, and count speckle or background &#39;&#39;&#39;&#39;noise&#39;&#39;&#39;&#39; on a surface such as a xerographic copy. The object surface is scanned simultaneously through a pair of apertures, one larger than the other. A photocell associated with each aperture provides an electrical pulse, proportionate in height to its illumination. Sufficient light from the copy surface through the larger (control) aperture signals its photocell to keep open a gate circuit. Simultaneously, a signal received through the smaller (counter) aperture is counted as &#39;&#39;&#39;&#39;noise.&#39;&#39;&#39;&#39; If the control aperture and its photocell receive light below a certain threshold level, (as when a print character is scanned) the gate circuit is closed and signals from the counter aperture are not counted.

United States Patent [191 Bauer INSTRUMENT FOR SCANNING DOCUMENT FORQUALITY [75] Inventor: George T. Bauer, Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22 Filedz Dec. 15, 1972 2: Appl. No.: 315,734

[52] US. Cl 356/200, 356/222, 250/571 J. L. Craft, Device for RapidChecking IBM [111 3,820,900 June 28, 1974 Technical Disclosure Bulletin,Feb. 1965.

Primary Examiner-Ronald L. Wibert 57 ABSTRACT An apparatus to scan,detect, and count speckle or background noise on a surface such as axerographic copy. The object surface is scanned simultaneously through apair of apertures, one larger than the other. A photocell associatedwith each aperture provides an electrical pulse, proportionate in heightto its illumination. Sufficient light from the copy surface through thelarger (control) aperture signals its photocell to keep open a gatecircuit. Simultaneously, a signal received through the'smaller (counter)aperture is counted as noise. If the control aperture and its photocellreceive light below a certain threshold level, (as when a printcharacter is scanned) the gate circuit is closed and signals from thecounter aperture are not counted.

ll Claim, 2 Drawing Figures 6010 F Pulse .C/rcu/I Height (Mu/f/v/brafodAnalyzer Power Supply PATENTEDJUHZB I914 3,820,900

Control 7 Q 5 Phofomulfl'pllbr 5 32 g 34- Gate Pulse 22 Circuit Height(Mu/f/wbrafor) Ana/per 24 4 30 Power Supply 1. SCANNING DOCUMENT FORBACKGROUND OF THE INVENTION This invention relates to instruments forthe detection and measurement of speckle or noise on specimen surfaces.More particularly, this invention relates to an instrument for thescanning of copy surface, such as the surface of xerographic copy, todetermine the presence and level of low density background noise on thecopy.

In the prior art, microphotometers are used to measure the granularityof photographic images. Fluctuations of transmitted (or reflected) lightare measured while the image is scanned and from the results thegranularity can be calculated. The scanning is typically not total butrandom sampling, and the method is statistical.

In xerography, a method more closely related to subjective observationsis desirable for the measurement and interpretation of low densitybackground noise. The presence of large toner particles on a document ismaterial to the quality'of images. To relate the number and sizedistribution of large particles to the image quality, it is necessary toscan a large area of the document or, preferably, the entire document.Present scanning microphotorneters are relatively slow and moreimportantly they scan both printed text andv background creatingproblems in the evaluation of the results.

SUMMARY OF THE INVENTION It is an object of this invention to provide aninstrument capable of scanning a document for background noise whileautomatically overlooking desired print characters.

Further objects, advantages and features of this invention will becomeapparent from the following description of one embodiment, given inconnection with the accompanying drawings.

The present invention is practiced in one form by a pair of scanningapertures exposed to a copy surface.

I The two apertures scan the same or adjacent areas of scanningapparatus 2. As shown, mechanism 6 is a drum capable of rotation andaxial translation to effect scanning motion. The details of mechanism 6are not material to this invention, and any known mechanism to effectthe desired relative motion between scanning cuit is closed and signalsfrom the counter aperture are not counted.

DRAWING FIG. I is a somewhat schematic diagram of a scanning apparatusaccording to this invention.

FIG. 2 shows a side by side comparison of the two scanning apertures,indicated in operative relationship to a copy character.

DESCRIPTION Referring now to FIG. 1, a scanning apparatus is indicatedgenerally at 2 and is shown in operative position relative to an objectsurface or document 4 mounted on a suitable mechanism 6 for movementrelative to the apparatus 2 and object surface 4 may be used.

Scanning apparatus 2 includes an objective lens 14 disposed adjacent theobject surface 4 on an optical axis 18. Behind the objective 14 islocated a beam divider 12 from which the optical axis 18 is divided intotwo branches ll'8t and l8r. Outwardly of beam divider 112, branch l8t ofoptical path 18 includes, in optical I alignment a, projection lens 20,a mask 22 defining a control aperture 24, and a control photomultiplier8. Similarly, branch 18r of optical path 18 includes, in opticalalignment, a projection lens 20, a mask 26 defining a counter aperture28, and a counter photomultiplier llt). All of the elements from theobjective 14 to the photomultipliers 8 and are mounted on a suitablesupport structure 16. Lenses 14 and 20 image the scan surface at theapertures 24 and 28.

Apertures 24 and 28 may be optically superposed relative to theobjective lens 14 bythe beam divider 12 so that they simultaneouslyalign with the same portion of the scan image (though aperture 24, beingthe larger, covers more). In other words,- apertures 24 and 28 may besimilarly located with respecttobranches l8t and tively connected to,and in control of, av multitivibrator gate circuit 32. Counterphotomultiplier 10 is operatively connected, through the gate circuit32, to a pulse height analyzer 34. A photoelectric signal above athreshold level from the control photomultiplier 8 maintains the gatecircuit 32 open. When gate circuit 32 is open, a signal from the counterphotomultiplier I0 is transmitted to pulse height analyzer v34.

Referring now to FIG. 2, the apertures 24 and 28 are representedschematically side-by-side and in associa-' tion with a pr'intcharacter40 on the object surface. Apertures 24 and 28 are shown hereside-by-side, though as stated above they may also be superposed withrespect to the objective lens 14. Control photomultiplier 8 is exposedto light through aperture 24 and if the light or optical signal receivedthrough aperture 28), as represented by the dotted line. Projection ofeven a small area of character 40 onto the counter aperture 28 causes anoptical signal to thecounter photomultiplier 10. Without the gatecircuit 32 this signal at It) would transmit to pulse analyzer 34 and becounted. However,the character 40 .is also projected through the controlaperture 24 which, being offset and larger than aperture 28 senses alarger area of the character 40. The decrease in optical signalgenerated by this decreased illumination through the aperture 24 causes3 i the control photomultiplier 8 to close the gate circuit 32 so thatthe signal from the counter photomultiplier 10 is not transmitted to thepulse analyzer 34. The desired print character 40 is thus not counted asbackground noise or speckle. By off-setting the light apertures and byhaving the larger'aperture control the gate circuit 32 this apparatusacts as a go-not go gateto sort out and count only signals belowacertain size.

The foregoing description of this invention is given by way ofillustration and not of limitation. For example, the scanning apertureshave been shown as rectangular but they may as well be square, circularor most any other convenient geometry. The concept and scope of theinvention are limited only by the following claims and equivalentsthereof which may occur to others skilled in the art.

What is claimed is:

1. A scanning apparatus to detect and count speckle on an object surfaceincluding:

an objective lens disposed on an optical axis relative to said objectsurface for scanning said object surface,

a beam divider disposed in said optical axis behind said objective lensto divide said optical axis into transmitted and reflected components,

a control aperture disposed along one of said components of said opticalaxis in conjugate relationship to said object surface,

a counter aperture, smaller than said control aperture, disposed alongthe other of said components of said optical axis in conjugaterelationship to said object surface,

said control aperture and said counter aperture being partiallyoptically superposed relative to said optical axis,

a control photosensitive element in optical communication with saidcontrol aperture, said control photosensitive element operativelyconnected to a gate circuit and maintaining said gate circuit open whenexposed to light above a threshold level and closing said gate circuitwhen exposed to light below said threshold level so that said gatecircuit is either open or closed,

a counter photosensitive element in optical communication with saidcounter aperture, said counter photosensitive element operativelyconnected, through said gate circuit, to a pulse counter whereby signalsfrom said counter photosensitive element are counted when said gatecircuit is open and said signals are not counted when said gate circuitis closed.

1. A scanning apparatus to detect and count speckle on an object surfaceincluding: an objective lens disposed on an optical axis relative tosaid object surface for scanning said object surface, a beam dividerdisposed in said optical axis behind said objective lens to divide saidoptical axis into transmitted and reflected components, a controlaperture disposed along one of said components of said optical axis inconjugate relationship to said object surface, a counter aperture,smaller than said control aperture, disposed along the other of saidcomponents of said optical axis in conjugate relationship to said objectsurface, said control aperture and said counter aperture being partiallyoptically superposed relative to said optical axis, a controlphotosensitive element in optical communication with said controlaperture, said control photosensitive element operatively connected to agate circuit and maintaining said gate circuit open when exposed tolight above a threshold level and closing said gate circuit when exposedto light below said threshold level so that said gate circuit is eitheropen or closed, a counter photosensitive element in opticalcommunication with said counter aperture, said counter photosensitiveelement operatively connected, through said gate circuit, to a pulsecounter whereby signals from said counter photosensitive element arecounted when said gate circuit is open and said signals are not countedwhen said gate circuit is closed.